1. Field
The present disclosure relates to an apparatus and method for treating a surface of a strip casting twin roll.
2. Description of Related Art
FIG. 1 is a schematic view illustrating a general twin roll strip caster of the related art.
As illustrated in FIG. 1, in the general twin roll strip caster of the related art, a molten steel pool 8 is formed by supplying molten steel, through a nozzle 4, to a space surrounded by twin rolls 1 and 1′ and edge dams 2 attached to both sides of the twin rolls 1 and 1′, and as the twin rolls 1 and 1′ are rotated, the molten steel is rapidly solidified by a heat flux into the twin rolls 1 and 1′ from the molten steel contacting the twin rolls 1 and 1′, thereby forming a strip 7.
Since the strip 7 manufactured using the twin roll strip caster of the related art as described above has a low thickness within the range of about 2 mm to about 6 mm, shells solidified at an early stage of the casting process have a significant influence on surface properties of the strip 7. That is, since molten steel makes contact with casting rolls for a very short period of time, solidified shells have an uneven thickness, and thus defects such as cracks or overlap defects may be formed in the surface of a strip. In this case, a subsequent rolling process may be negatively affected, and thus a final product may have poor gloss and a low value.
To address this, dimples are formed in the surfaces of casting rolls through a surface treatment process by various methods so as to prevent the formation of defects in a strip, such as surface cracks, by effectively distributing thermal stress in the strip during a strip casting process. Such dimples lead to the formation of gas gaps functioning as adiabatic layers between cooling rolls and solidified shells, thereby reducing heat extraction from the cooling rolls and guaranteeing gradual cooling of the solidified shells. In addition, since shells start to solidify from peripheral regions (edge regions) of the dimples, the thickness of the shells may be uniform.
Such dimples are formed by various methods. For example, surfaces of casting rolls may be machined using a laser to form dimples.
According to the above-mentioned laser machining method for machining surfaces of casting rolls using a laser, a geometric pattern having a predetermined size is formed on a cylindrical casting roll. However, after the cylindrical casting roll is rotated once, the remaining amount of a joining region of the pattern is not constant, and thus it is difficult to exactly connect joining portions of the pattern. Particularly, each casting roll weighs more than 20 tons and has a large machining area (about 1340 mm in width×about 1280 mm in diameter). Thus, many pieces of equipment and a great degree of effort are required to finish a fine machining process within an intended period of time with an intended degree of precision. In general, when a casting roll is rotated, it is very difficult to obtain positional precision within the range of 1 mm or less using a driving unit.
When the final line of a casting roll is machined, ends of the final line and the first line have to be exactly coincident with each other. However, it is impossible to exactly align the ends of the final and first lines because the circumference of a casting roll having a diameter D is an irrational number (π×D) and the unit height h of dimples is a rational number.